How to: Demolish a truss bridge

Like the people cheering at about :25 into this video, I'm a sucker for dramatic explosions. This one comes from Texas, where the transportation department blew up an old bridge in the city of Marble Falls on March 17th. Also, apparently, it's warm enough in Texas that multiple gentlemen could watch a bridge explode from the comfort of their jet skis.

Most excellent! All my day needs now would be a Go-Pro POV from an RC racer zipping across the bridge at the moment of detonation, but I guess some spoilsport would have discouraged anything radio-controlled from being near a bridge wired with explosives.

I, for one, would accept any interference caused. That’s why they don’t put me in charge.

It seems pretty nuts that they decided the most efficient way to remove a bridge is blow it up and spend months dragging the remains out of the river.. during which period I’ll assume no river traffic will be allowed to pass through.

Or maybe they load an electromagnet crane onto a barge and hoover the scraps up?

From what little I’ve read, yes: they ran the numbers, and it turns out to be a *lot* cheaper, as well as easier, faster and safer to do it this way.

Crap falling in rivers and needing to be whipped out with a crane is apparently an everyday thing: while dismantling an old bridge is fraught with complexities, engineering challenges, and legal and health&safety stumbling blocks.

“it’s warm enough in Texas that multiple gentlemen could watch a bridge explode from the comfort of their jet skis”
Fun as that would assuredly be, I’d settle for ‘warm enough for liquid water to actually be a thing’ right now… :(

Funnily enough, I’d settle for ‘cold enough for liquid water to actually be a thing’. I’ve tried putting ice on my outdoor plants to slow-water on hot days, but it evaporates without ever liquifying enough to drip.

Guys, its Texas… It could be 20F out there and some good ol boy from “a big college with very “high class” engineering students” would be out there on his jet ski trying to get the best angle on the boom. All things are possible with a little whiskey and coke.

I’m a bit curious about the two separate sound events. Frequency shouldn’t account that much for to alter the speed of sound… and you can see that the main explosions are happening before the charges are all finished triggering, yet you can hear that the initial sound is finished before the main charges go off.

That’d be a heck of a powerful EM blast (though maybe the bridge could be an antenna). What makes me think that’s not the case here is that the high frequency sound is delayed from the light itself, just not as much as the lower frequency explosion.

Maybe there was a loud device closer to the camera that was triggering the charges in a rapid fashion (loud relays?).

“……… With the PETN exploding at a rate of approximately 4 miles per second, any common length of det cord appears to explode instantaneously. It is a high-speedfuse which explodes, rather than burns, and is suitable for detonating high explosives, usually pentaerythritol tetranitrate (PETN, Pentrite). …. It is used to reliably and inexpensively chain together multiple explosive charges. Typical uses include mining, drilling, demolitions, and warfare…..”

Yeah, I’m guessing that the glowing loops that you can see progressing ahead of the explosions are the det cord. I will point out that a trail of gunpower laid on the floor goes pretty quickly too. Not 4miles per second, but more FOOM! than sizzle. You’re not going to out run it.